Radio frequency (RF) transmitters in wireless communication devices consume a large portion of power. More specifically, RF transmitters have to transmit and therefore, consume a large portion power. Efficient use of the RF spectrum requires the use of RF signals with variable envelope and phase. These signals are typically produced with high linearity using class AB amplifiers, which are inefficient. Variations in battery voltages from charged to discharged make the class AB amplifier even less efficient. The class AB amplifier has to be biased such that it can provide the peak power without clipping at the lowest battery voltage. Consequently, at the highest battery voltage the efficiency is lowered even for peak-power output.
In one known technique, a cascaded buck and boost converter is used. The control operates in a manner that the converter is either in buck or boost (BOB) mode on a cycle-by-cycle basis. It transitions between the modes to modulate the power supply of a variable envelope RF power amplifier. While this technique is an improvement over the class AB amplifier, it is desirable to increase efficiency and tracking bandwidth.
As such, it is desirable to provide a method and apparatus that tracks envelopes of RF signals in a more efficient manner. It is also desirable to provide a method and apparatus that exhibits an increased RF envelop tracking bandwidth.